It is typical of manholes to have step rungs placed in the manhole structure to provide a continuous ladder of equally placed step rungs within the manhole. The rungs for the ladder are typically spaced 12 inches (30.5 cm) apart. The maximum allowable distance from the top of the manhole frame to the first step rung in the manhole is 20 inches (51 cm). The manhole frame adjustment space between the top of the concrete manhole and the underside of the manhole frame is typically filled by layering bricks or concrete rings and mortar. A step rung is typically placed in this area so as to continue the even step rung placing toward the top of the manhole frame. The top of the manhole frame is typically set flush with the asphalt or concrete surface of the roadway. The adjustment area below the base of the frame is typically maintained at the same diameter as the opening of the top of the concrete manhole opening. Step rungs placed into the wall of the adjustment space must be embedded three inches (7.6 cm) deep and extend four inches (10 cm) outward from the point of embedment. The placement of the step rung into the adjustment space reduces the space available for a worker passing the step rung at this point. The spacing of the step rung and the allowable minimums of the reduced area between the outermost extension of the embedded step rung and the opposite side of the wall of the adjustment area however may still fall within the generally accepted Occupational Health and Safety standards.
Some jurisdictions state that if a handhold is placed into the manhole frame adjustment area, the distance from the top of the manhole frame to the first step rung in the manhole may be extended from twenty inches (51 cm) to twenty six inches (66 cm). Handholds are not typically required to be spaced evenly as with step rung requirements and therefore may be spaced considerably above the last designated step rung in the manhole and still comply with Occupational Health and Safety standards. It is therefore desirable to meet these safety requirements using a method that reduces the width of the access area of the manhole frame adjustment area to a lesser degree than is now typical using the continuous step rung procedure.
The present inventor is also the inventor of the manhole casting positioning apparatus disclosed in U.S. Pat. No. 4,666,333 issued May 19, 1987. Manholes for sewers and the like are typically assembled by stacking a number of precast, cylindrical concrete barrel sections to approximately the desired height. In order to allow some adjustability of the placement of the iron manhole casting on the end of the manhole in relation to the road grade, a 1-inch (2.54 cm) to 8-inch (20.3 cm) space is typically left between the manhole and the iron casting. Previously this space was filled with layers of bricks, which is expensive and time consuming. The apparatus disclosed in U.S. Pat. No. 4,666,333 provides a two-piece form, consisting of an inner and outer sleeve, which replaces the brick and mortar method.
In the inventor's apparatus disclosed in U.S. Pat. No. 4,666,333, the inner sleeve may consist of a single plastic piece joined end-to-end to form a cylinder which is expandable by means of turnbuckle-type expansion mechanisms. The outer sleeve may be in the form of a belt with a receptacle at one end through which the other end passes and is secured to form a cylinder. The inner sleeve is first expanded into the manhole opening and set to the required slope. The casting is mounted on the inner sleeve, and the outer sleeve, which has a diameter greater than that of the base of the casting, is placed around the casting. Concrete is then poured between the inner and outer sleeves and up over the base of the casting. After the concrete has set the outer sleeve is removed, and the inner sleeve can be removed or left in place.
The foregoing examples of the related art and limitations related thereto are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.